docs for unstable_enableSyncVoidMethods (facebook#40779)

Summary:
Pull Request resolved: facebook#40779

Changelog: [Internal]

adding docs to unstable_enableSyncVoidMethods config related methods

Reviewed By: mdvacca, cipolleschi

Differential Revision: D50160367

fbshipit-source-id: 6fc825f7225f11909e0749c75d03b2ddadc3d5aa

Author: philIip

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/config/ReactFeatureFlags.java

@@ -36,6 +36,10 @@ public class ReactFeatureFlags {
    */
   public static volatile boolean unstable_useTurboModuleInteropForAllTurboModules = false;
 
+  /**
+   * By default, native module methods that return void run asynchronously. This flag will make
+   * execution of void methods in TurboModules stay on the JS thread.
+   */
   public static volatile boolean unstable_enableTurboModuleSyncVoidMethods = false;
 
   /**

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/internal/turbomodule/core/TurboModuleManagerDelegate.java

@@ -70,6 +70,7 @@ public boolean unstable_shouldRouteTurboModulesThroughLegacyModuleInterop() {
     return false;
   }
 
+  /* Can TurboModule methods that return void execute on the JS thread? */
   public boolean unstable_enableSyncVoidMethods() {
     return false;
   }